Method for producing arylsulphonic acid isocyanates

ABSTRACT

The present invention relates to a process for preparing arylsulfonyl isocyanates by reacting an arylsulfonamide with phosgene in the presence of a catalytically effective amount of an alkyl isocyanate.

The present invention relates to a process for preparing arylsulfonylisocyanates by reacting an arylsulfonamide with phosgene in the presenceof a catalytically effective amount of an alkyl isocyanate.

Arylsulfonyl isocyanates are industrially important intermediates in thepreparation of a large number of compounds, in particular herbicides.There is a need for processes for preparing them which not only give ahigh yield and productivity but also display a high reaction rate andthus short reactor occupation times.

U.S. Pat. No. 4,379,769 describes a process for preparing arylsulfonylisocyanates by phosgenation of arylsulfonamides in the presence of acatalytically effective amount of an alkyl isocyanate and acatalytically effective amount of a tertiary amine base.

In Angew. Chem. 78, pp. 761-769 (1966), H. Ulrich and A. A. R. Sayighdescribe the preparation of arylsulfonyl isocyanates, in which either asulfonamide is reacted with a readily available alkyl isocyanate to formthe urea derivative and the latter is subsequently phosgenated, with thestarting isocyanate being recovered, or else a catalytic amount of theisocyanate is added to the sulfonamide for the phosgenation.

Pestycydy 1989, (4), 1-7; ISSN: 0208-8703 describes the preparation of2-chlorobenzenesulfonyl isocyanate by phosgenation of the correspondingsulfonamide in the presence of butyl isocyanats and inortho-dichlorobenzene as solvent.

Res. Discl. (1983), 23210, p. 261; ISSN: 0374-4353, describes a processfor preparing arylsulfonyl isocyanates by phosgenation ofarylsulfonamides, in which a mixture of an alkyl isocyanate and anarylsulfonyl isocyanate is used as catalyst. The arylsulfonyl isocyanateformed as product can be recirculated to the reaction in catalyticallyeffective amounts.

Journal of Polymer Science, Vol. 13 (1975), pp. 267-268, teaches the useof a mixture of ortho-dichlorobenzene and cellosolve acetate as solventin the synthesis of m-phenylenedisulfonyl diisocyanates by phosgenationof m-benzenedisulfonamide in the presence of catalytic amounts of analkyl or aryl isocyanate.

It is an object of the present invention to provide an improved processfor preparing arylsulfonyl isocyanates. The reaction times involvedshould be very short and/or the formation of undesirable by-productsshould be minimized.

We have found that this object is achieved by reacting anarylsulfonamide with phosgene in the prescence of catalyticallyeffective amounts of an alkyl isocyanate when the reaction is carriedout in the additional presence of a catalytically effective amount of aprotic acid or a salt thereof and/or the phosgene is introduced in sucha way that the concentration of alkylarylsulfonylurea in the reactionmixture does not go below a minimum concentration during the time ofaddition.

The present invention accordingly provides a process for preparingarylsulfonyl isocyanates by reacting an arylsulfonamide with phosgene,in which the arylsulfonamide and a catalytically effective amount of analkyl isocyanate are placed in a reaction zone, forming analkylarylsulfonylurea as intermediate, and the phosgene is fed into thereaction zone, wherein

-   -   a) the reaction is carried out in the presemce of a        catalytically effective amount of a protic acid which has at        least one hydroxy group capable of protolysis or a salt thereof        and/or    -   b) the phosgene is introduced in such a way that the        concentration of alkylarylsulfonylurea in the reaction zone does        not go below 100 ppm during the time of addition.

The process of the present invention is generally suitable for preparingarylsulfonyl isocyanates having unsubstituted or substituted arylradicals. These are, for example, arylsulfonyl isocyanates of theformula I

where

-   -   R¹, R² and R³ are each, independently of one another, hydrogen        or in each case substituted or unsubstituted alkyl, cycloalkyl,        heterocycloalkyl, aryl or hetaryl or WCOOR^(a), WCOO⁻M⁺,    -   W(SO₃)R^(a), W(SO₃)⁻M⁺, WPO₃(R^(a))(R^(b)), W(PO₃)²⁻(M⁺)₂,        WOR^(a), WSR^(a), (CHR^(b)CH₂O)_(x)R^(a), W-halogen, WNO₂,        WC(═O)R^(a) or WCN,    -   where    -   W is a single bond, a heteroatom or a divalent bridging group        having from 1 to 20 bridge atoms,    -   R^(a), E¹, E², E³ are identical or different radicals selected        from among hydrogen, alkyl, cycloalkyl, heterocycloalkyl, aryl        and hetaryl,    -   R^(b) is hydrogen or C₁-C₈-alkyl, preferably methyl or ethyl,    -   M⁺ is a cation equivalent,    -   X⁻ is an anion equivalent and    -   x is an integer from 1 to 20,        where two adjacent radicals R¹, R² and R³ together with the        carbon atoms of the benzene ring to which they are bound may        also form a fused ring system having 1, 2 or 3 further rings.

For the purposes of the present invention, the expression ‘alkyl’ refersto straight-chain and branched alkyl groups. These are preferablystraight-chain or branched C₁-C₂₀-alkyl groups, more preferablyC₁-C₁₂-alkyl groups and particularly preferably C₁-C₈-alkyl groups andvery particularly preferably C₁-C₄-alkyl groups. Examples of alkylgroups are, in particular, methyl, ethyl, propyl, isopropyl, n-butyl,2-butyl, sec-butyl, tert-butyl, n-pentyl, 2-pentyl, 2-methylbutyl,3-methylbutyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl,2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 2-hexyl, 2-methylpentyl,3-methylpentyl, 4-methylpentyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl,2,3-dimethylbutyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl,3,3-dimethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl,1-ethylbutyl, 2-ethylbutyl, 1-ethyl-2-methylpropyl, n-heptyl, 2-heptyl,3-heptyl, 2-ethylpentyl, 1-propylbutyl, octyl, nonyl, decyl.

The expression alkyl also encompasses substituted alkyl groups.Substituted alkyl groups preferably have 1, 2, 3, 4 or 5, in particular1, 2 or 3, substituents selected from among cycloalkyl, aryl, hetaryl,halogen, NO₂ CN, acyl, carboxyl, carboxylate, —SO₃H and sulfonate.

The expression cycloalkyl encompasses unsubstituted and substitutedcycloalkyl groups. The cycloalkyl group is preferably C₅-C₇-cycloalkylgroup such as cyclopentyl, cyclohexyl or cycloheptyl.

If the cycloalkyl group is substituted, it preferably has 1, 2, 3, 4 or5, in particular 1, 2 or 3, substituents selected from among alkyl,alkoxy, halogen, NO₂, CN, acyl, carboxyl, carboxylate, —SO₃H andsulfonate.

For the purposes of the present invention, the expressionheterocycloalkyl encompasses saturated, cycloaliphatic groups whichgenerally have from 4 to 7, preferably 5 or 6 ring atoms and in which 1or 2 of the ring carbons have been replaced by heteroatoms selected fromamong the elements oxygen, nitrogen and sulfur and which may besubstituted. If they are substituted, these heterocycloaliphatic groupscan bear 1, 2 or 3 substituents, preferably 1 or 2 substituents,particularly preferably 1 substituent, selected from among alkyl, aryl,alkoxy, halogen, NO₂, CN, acyl, COOR^(a), COO⁻M⁺ and SO₃R^(a),preferably alkyl. Examples of such heterocycloaliphatic groups arepyrrolidinyl, piperidinyl, 2,2,6,6-tetramethylpiperidinyl,imidazolidinyl, pyrazolidinyl, oxazolidinyl, morpholidinyl,thiazolidinyl, isothiazolidinyl, isoxazolidinyl, piperazinyl,tetrahydrothiophenyl, tetrahydrofuranyl, tetrahydropyranyl, dioxanyl.

Aryl is preferably phenyl, tolyl, xylyl, mesityl, naphthyl, anthracenyl,phenanthrenyl, naphthacenyl, in particular phenyl or naphthyl.

Substituted aryl radicals preferably have 1, 2, 3, 4 or 5, inparticular, 1, 2 or 3, substituents selected from among alkyl, alkoxy,carboxyl, carboxylate, —SO₃H, sulfonate, halogen, NO₂, CN and acyl.

Hetaryl is preferably pyrrolyl, pyrazolyl, imidazolyl, indolyl,carbazolyl, pyridyl, quinolinyl, acridinyl, pyridazinyl, pyrimidinyl orpyrazinyl.

Substituted hetaryl radicals preferably have 1, 2 or 3 substituentsselected from among alkyl, alkoxy, carboxyl, carboxylate, —SO₃H,sulfonate, halogen, NO₂, CN and acyl.

What has been said above with regard to alkyl, cycloalkyl and arylradicals applies analogously to alkoxy, cycloalkyloxy and aryloxyradicals.

Halogen is preferably fluorine, chlorine, bromine or iodine, preferablyfluorine, chlorine or bromine.

For the purposes of the present invention, carboxylate and sulfonate arepreferably derivatives of a carboxylic acid function or a sulfonic acidfunction, in particular a metal carboxylate or sulfonate, a carboxylicester or sulfonic ester function or a carboxamide or sulfonamidefunction. They include, for example, esters with C₁-C₄-alkanols such asmethanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol andtert-butanol.

M⁺ is a cation equivalent, i.e. a monovalent cation or that part of apolyvalent cation which corresponds to a single positive charge. M⁺ ispreferably an alkali metal cation, e.g. Li⁺, Na⁺ or K⁺, or an alkalineearth metal cation, NH₄ ⁺ or a quaternary ammonium compound as can beobtained by protonation or quaternization of amines. Preference is givento alkali metal cations, in particular sodium or potassium ions.

X⁻ is an anion equivalent, i.e. a monovalent anion or that part of apolyvalent anion which corresponds to a single negative charge. X⁻ ispreferably a carbonate, carboxylate or halide, particularly preferablyCl⁻ or Br⁻.

x is an integer from 1 to 240, preferably an integer from 3 to 120.

Fused ring systems can be aromatic, hydroaromatic and cyclic compoundsjoined by fusion. Fused ring systems have two, three or more rings.Depending on the way in which the rings in fused ring systems arelinked, a distinction is made between ortho-fusion, i.e. each ringshares an edge or two atoms together with each adjacent ring, andperi-fusion in which a carbon atom belongs to more than two rings. Amongfused ring systems, preference is given to ortho-fused ring systems.

The process of the present invention is particularly useful forpreparing an arylsulfonyl isocyanate of the formula I.1

where

-   -   R¹ is an electron-withdrawing group, preferably a group selected        from among F, Cl, Br, NO₂, CF₂H, CF₂Cl₂, CHCl₂ and CF₃, and    -   R² is hydrogen, C₁-C₄-alkyl, C₁-C₄-alkoxy, F, Cl, Br or        C₁-C₄-alkylthio, where the alkyl radicals may bear 1, 2 or 3        halogen atoms.

The sulfonamides used as starting materials can be obtained by reactingthe corresponding sulfonyl chlorides with ammonia (M. Quaedvlieg inHouben-Weyl, “Methoden der organischen Chemie”, Georg Thieme Verlag,Stuttgart, vol. 9 (1955) 398-400, F. Muth, ibid., 605ff).

The corresponding sulfonyl chlorides for preparing the sulfonamides aregenerally obtained by a Meerwein reaction (diazotization of suitableamides and sulfochlorinated by means of sulfur dioxide in the presenceof copper salts as catalysts: F. Muth in Houben-Weyl, “Methoden derorganischen Chemie”, Georg Thieme Verlag, Stuttgart, vol. 9 (1955) 579,S. Pawlenko in Houben-Weyl, “Methoden der organischen Chemie”, GeorgThieme Verlag, Stuttgart, vol. E 11/2 (1985) 1069), from thecorresponding sulfonic acids (F. Muth in Houben-Weyl, “Methoden derorganischen Chemie”, Georg Thieme Verlag, Stuttgart, vol. 9 (1955) 564),by chlorosulfonation of suitable aromatic precursors (F. Muth, ibid., p.572) or by oxidative chlorination of low oxidation stage sulfurprecursors (mercaptans, diaryl disulfides, S-benzylmercaptans,thiocyanates (F. Muth, ibid., p. 580, S. Pawlenko, loc. cit., p. 1073).

The reaction rate in the phosgenation of arylsulfonamides canadvantageously be increased over that in processes known from the priorart when the reaction is carried out in the presence of a catalyticallyeffective amount of a protic acid which has at least one hydroxy groupcapable of protolysis or a salt thereof.

The amount of protic acid or salt thereof used is preferably from about0.05 to 1% by weight, particularly preferably from 0.1 to 0.5% byweight, based on the amount of arylsulfonamide used.

Suitable catalysts are generally compounds of carbon, nitrogen,phosphorus and sulfur which have at least one hydroxy group capable ofprotolysis and the salts thereof. The catalyst is particularlypreferably selected from among carboxylic acids, nitric acid, phosphinicacids, phosphonic acids, phosphoric acid and its monoesters anddiesters, sulfinic acids, sulfonic acids, sulfuric acid and itsmonoesters and the salts thereof.

Salts suitable as catalysts are preferably the alkali metal salts,especially the Li, Na and K salts.

Preference is given to using an organic sulfonic acid or a salt thereof,in particular an arylsulfonic acid or a salt thereof, for catalyzing thephosgenation. Particular preference is given to using a benzenesulfonicacid or an alkali metal salt thereof, especially sodiumbenzenesulfonate.

As an alternative to or in addition to the use of a catalyst in the formof a protic acid or a salt thereof, the reaction rate of thephosgenation of arylsulfonamides can be increased over that ofphosgenation processes known from the prior art when the phosgene isintroduced in such a way that the alkylarylsulfonylurea concentration inthe reaction zone does not go below 100 ppm, preferably 500 ppm, duringthe time of addition.

The alkylarylsulfonylurea is formed as an intermediate in the reactionzone from the initially charged arylsulfonamide and the alkyl isocyanateused as catalyst. On addition of the phosgene, the intermediate isconverted into the arylsulfonyl isocyanate wanted as product and thealkyl isocyanate used as catalyst is reformed.

In a useful embodiment, the introduction of the phosgene is commencedonly after the alkylarylsulfonylurea concentration in the reaction zonehas reached a value of 100 ppm.

In a further useful embodiment, not only the arylsulfonamide and thealkyl isocyanate but also the alkylarylsulfonylurea derived therefromare placed in the reaction zone. The amount of alkylarylsulfonylureainitially charged is then at least 100 ppm.

In a preferred embodiment, the introduction of the phosgene iscontrolled during the time of addition so that the alkylarylsulfonylureaconcentration in the reaction zone does not go below the desired value.A volume flow which is less than the maximum volume flow is preferablyused at the beginning of the time of addition. A reduced volume flow ispreferably used during not more than the first 40% of the time ofaddition, particularly preferably during not more than the first 30%, inparticular during not more than the first 20%. The stream having a flowless than the maximum volume flow can have a flow profile which isincreased in the form of a gradient or in one or more steps to themaximum volume flow. Preference is given to using a constant volume flowwhich is less than the maximum volume flow at the beginning of the timeof addition (step profile). The volume flow employed at the beginning ofthe time of addition is preferably 60%, particularly preferably 50%, ofthe maximum volume flow. Particular preference is given to a process inwhich not more than one tenth of the total amount of phosgene isintroduced during the first sixth of the time of addition.

Preference is given to using a volume flow less than the maximum volumeflow at the end of the time of addition. A volume flow which is lessthan the maximum volume flow is preferably used during not more than thelast 40% of the time of addition, particularly preferably during notmore than the last 30%, in particular during not more than the last 20%.The stream having a flow which is less than the maximum volume flow canhave a flow profile which is reduced from the maximum volume flow in theform of a gradient or in one or more steps. Preference is given to usinga constant volume flow which is less than the maximum volume flow at theend of the time of addition (step profile). The volume flow used at theend of the time of addition is preferably not more than 60%,particularly preferably not more than 50%, of the maximum volume flow.Particular preference is given to a process in which not more than onetenth of the total amount of phosgene is introduced during the lastsixth of the time of addition. If the phosgene is added at a constantvolume flow rate over the entire time of addition, the time of additionhas to be significantly increased over that in the above-described rampprocedure. Otherwise, there is appreciable formation of undesirableby-products such as arylsulfonyl chlorides, which results in a decreasein the yield of isocyanates.

In a particularly preferred embodiment of the process of the presentinvention, the reaction is carried out in the presence of acatalytically effective amount of a protic acid as described above or asalt thereof and the introduction of the phosgene is also controlled asdescribed above.

The alkyl isocyanate used as catalyst is preferably selected from amongC₄-C₁₀-alkyl isocyanates and C₅-C₈-cycloalkyl isocyanates, e.g. n-butylisocyanate, n-pentyl isocyanate, n-hexyl isocyanate, n-octyl isocyanate,n-decyl isocyanate and cyclohexyl isocyanate. Preference is given tousing n-butyl isocyanate. The amount of alkyl isocyanate used ispreferably in the range from 5 to 40 mol %, particularly preferably from10 to 30 Mol %, based on arylsulfonamide used.

The amount of phosgene used is preferably in the range from 100 to 250mol %, particularly preferably from 150 to 200 mol %, based onarylsulfonamide used.

The phosgenation is preferably carried out at from 100 to 175° C. Thepressure during the reaction is preferably ambient pressure, but thereaction can also be carried out at elevated or reduced pressures.

Typical reaction times are in a range from about 30 minutes to 24 hours,preferably from 1 to 12 hours.

The reaction is preferably carried out in solvents which are inerttoward the starting materials. Such solvents include, for example,aromatic hydrocarbons such as toluene, xylene and mesitylene,haloaromatics such as chlorobenzene, halogenated aliphatic hydrocarbonssuch as pentachloroethane, etc.

After the reaction is complete, the reaction mixture can be worked up bycustomary methods known to those skilled in the art. These include, forexample, measures for driving off excess phosgene, for example continuedheating or passage of a gas stream, for example an inert gas, throughthe reaction solution. The measures employed for the work-up alsoinclude customary methods of separating off the solvent used, e.g.distillation, if desired under reduced pressure. The process of thepresent invention gives high yields of arylsulfonyl isocyanates and highproduct purities. The arylsulfonyl isocyanates obtained by the processof the present invention are well-suited to the preparation ofherbicides.

The invention is illustrated by the following nonrestrictive examples.

EXAMPLE 1

112.6 g (0.5 mol) of 2-trifluoromethylbenzenesulfonamide, 360 mg ofsodium benzenesulfonate and 9.9 g (0.1 mol) of n-butyl isocyanatetogether with 400 g of ortho-xylene are placed in a 1 l flask providedwith a reflux condenser and gas inlet tube and the mixture is heated toan internal temperature of 143° C. 12.2 g of phosgene are fed in at anessential constant volume flow over a period of 2 hours. 63.8 g ofphosgene are subsequently fed in at a maximum volume flow over a furtherperiod of 120 minutes. A further 11 g of phosgene are subsequently fedin at a constant, reduced volume flow over a period of 2 hours. Theyield of 2-trifluoromethylsulfonyl isocyanate was 85% of theory.

EXAMPLE 2 (COMPARISON)

The procedure of Example 1 was repeated, except that 87 g of phosgenewere fed in at a constant volume flow over a period of 7 hours. Theformation of about 5% of 2-trifluoromethylsulfonyl chloride was detectedby means of HPLC, and the yield of 2-trifluoromethylsulfonyl isocyanatewas about 80% of theory.

1. A process for preparing arylsulfonyl isocyanates, in which anarylsulfonamide and a catalytically effective amount of an alkylisocyanate are placed in a reaction zone, forming analkylarylsulfonylurea as intermediate, and phosgene is fed into thereaction zone, wherein a) the phosgenation reaction is carried out inthe presence of a catalytically effective amount of a protic acid whichhas at least one hydroxy group capable of protolysis or a salt thereofand/or b) the phosgene is introduced in such a way that theconcentration of alkylarylsulfonylurea in the reaction zone does not gobelow 100 ppm during the time of addiction.
 2. A process as claimed inclaim 1, wherein a protic acid selected from among carboxylic acids,nitric acid, phosphinic acids, phosphonic acids, phosphoric acid and itsmonoesters and diesters, sulfinic acids, sulfonic acids, sulfuric acidand its monoesters and salts thereof is used in step a).
 3. A process asclaimed in claim 1, wherein an organic sulfonic acid or an alkali metalsalt thereof is used in step a).
 4. A process as claimed in claim 1,wherein a phosgene stream having a volume flow which is less than themaximum phosgene flow used is fed into the reaction zone during thefirst 40% of the time of addition.
 5. A process as claimed in claim 1,wherein a phosgene stream having a volume flow which is less than themaximum phosgene flow used is fed into the reaction zone during the last40% of the time of addition.
 6. A process as claimed in claim 1,wherein, in step b), not more than one tenth of the total amount ofphosgene is introduced during the first sixth of the time of addition.7. A process as claimed in claim 1, wherein, in step b), not more thanone tenth of the total amount of phosgene is introduced during the lastsixth of the time of addition.
 8. A process as claimed in claim 1,wherein b) the phosgene is introduced in such a way that theconcentration of alkylarylsulfonylurea in the reaction zone does not gobelow 100 ppm during the time of addition, and optionally a) thereaction is carried out in the presence of a catalytically effectiveamount of a protic acid which has at least one hydroxy group capable ofprotolysis or a salt thereof.
 9. A process as claimed in claim 1,wherein a) the reaction is carried out in the presence of acatalytically effective amount of a protic acid which has at least onehydroxy group capable of protolysis or a salt thereof, and optionally b)the phosgene is introduced in such a way that the concentration ofalkylarylsulfonylurea in the reaction zone does not go below 100 ppmduring the time of addition.
 10. A process as claimed in claim 1,wherein a) the reaction is carried out in the presence of acatalytically effective amount of a protic acid which has at least onehydroxy group capable of protolysis or a salt thereof, and b) thephosgene is introduced in such a way that the concentration ofalkylarylsulfonylurea in the reaction zone does not go below 100 ppmduring the time of addition.
 11. A process as claimed in claim 1,wherein, in stage (a), the reaction is carried out in the presence of acatalytically effective amount of the salt of the protic acid which hasat least one hydroxy group capable of protolysis.
 12. A process asclaimed in claim 8, wherein, in stage (a), the reaction is carried outin the presence of a catalytically effective amount of the salt of theprotic acid which has at least one hydroxy group capable of protolysis.13. A process as claimed in claim 9, wherein, in stage (a), the reactionis carried out in the presence of a catalytically effective amount ofthe salt of the protic acid which has at least one hydroxy group capableof protolysis.
 14. A process as claimed in claim 10, wherein, in stage(a), the reaction is carried out in the presence of a catalyticallyeffective amount of the salt of the protic acid which has at least onehydroxy group capable of protolysis.